The present invention relates to processing of soybeans wherein the soybeans are subjected to a breaking or crushing action in order to be flaked prior to extraction in a method for the recovery of soybean oil and soybean meal.
Soybeans possess a lecithin-containing oil in an amount of approximately 20% and protein in an amount of approximately 36%. During the processing of the soybeans there is accomplished the separation, resulting in recovery of the oil and the extracted material is used as feed or fodder. The extraction typically is accomplished through the use of a solvent. At the present time there are fabricated two types of meal, a so-called normal meal having a protein content of approximately 44% and a high-grade meal whose protein content is in the order of approximately between 49 to 50%. In the case of the high-grade meal there is obtained an increase in the protein content by separating the soybean hulls or shells which predominantly contain fibres and other ballast materials.
With the present day conventional method the soybeans are headed to approximately 90.degree. C. in a shaft drier-cooler and subsequently cooled in the cooler to a temperature of approximately 10.degree. C. above the ambient temperature. The purpose of this process step, resulting in a reduction in the moisture content of approximately 2 percent-by-weight, is to render the hulls brittle, cause them to split or burst and to detach from the actual seeds or kernels of the soybeans. However, in order to obtain a satisfactory separation or dehulling it is necessary to temper all of the soybeans for at least 48 hours prior to further processing. This is accomplished in temper silos or bins which constitute large size and expensive structures. After the tempering operation the entire loy of soybeans is crushed or broken by means of two-stage corrugated roll beds while in a cold condition for the purpose of freeing the hull or shell pieces and the seed portion or kernels. The broken material is separated by means of vibration sieves into seed portions and hulls or shells. The hulls are removed by a suction action in accordance with the vacuum cleaner principle. This suced fraction however still contains much too great an amount of protein and oil-containing seed particles and therefore additionally must be separated in two further stages into hulls and seed portions. The material cleaned from the pods or shells is subsequently conditioned. To that end the product temperature is again elevated to approximately 60.degree.-65.degree. C., so that there is lowered the viscosity of the oil encapsulated in cells and the previously hard soybean fractures become plastic in order that at the subsequent flaking roll bed the fractured pieces can be rolled with the least possible expenditure in energy, into stable thin flakes of approximately 0.3 mm thickness.
The just described conventional method appears to be uneconomical for a number of different reasons. On the one hand, the material is heated-up, thereafter however immediately cooled and fractured or broken in a cold condition at the corrugated rolls or rollers. These operations expose the equipment to considerable mechanical loads which, in turn, impairs its service life, and following the crushing or fracturing operation the material is again heated to approximately 65.degree. C. Hence, an appreciable amount of work and energy is associated with the practice of this prior art method. Furthermore, this method is discontinuous by virtue of the necessity of storing the soybeans in tempering silos. As mentioned, these tempering silos are large and expensive structures.